Carbon and Oxygen in Nearby Stars: Keys to Protoplanetary Disk Chemistry

The California Planet Search has collected thousands of spectra with the mighty 10m Keck Telescope to search for planets around other stars. These spectra, however, contain a wealth of information in addition to a star’s radial velocity. I measured the abundances of carbon and oxygen in a large number of stars using a LTE spectrum synthesizer called SME (Spectroscopy Made Easy). I found that 10% of stars have C/O>1. Such stars enriched in carbon could host radically different small planets, composed of carbides, diamond, and tar rather than silicates which are common among the small planets in the solar system.

ApJ Paper

C/O plotted against [Fe/H] for 457 stars with reliable C and O measurements. 10% stars have C/O > 1.   The panel at right shows marginal distributions of C/O in host and non-host stars.  Planet host and non-host populations are consistent with being drawn from the same distribution.  This is in stark contrast to the top panel which shows the well-known planet-metallicity correlation (Santos et al., 2004; Fischer & Valenti 2005).

C/O plotted against [Fe/H] for 457 stars with reliable C and O measurements. 10% stars have C/O > 1. The panel at right shows marginal distributions of C/O in host and non-host stars. Planet host and non-host populations are consistent with being drawn from the same distribution. This is in stark contrast to the top panel which shows the well-known planet-metallicity correlation (Santos et al., 2004; Fischer & Valenti 2005).